<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <script src="vue.js"></script>
    <title>Title</title>
</head>
<body>
<div id="box">
    <input type="text" v-model="msg | filterhtml">
    <br>
    <div v-html="msg"></div>
</div>
</body>
<script>
    Vue.filter('filterhtml',{
        read: function (value) {
            return input.replace(/<[^<+]>/g,'');
        },
        write: function (value) {
            return '<strong>'+value+'</strong>';
        }
    })
    var app = new Vue({
        el: '#box',
        data: {
            msg: '<strong>welcome</strong>'
        },
    })
</script>
</html>